Taiwan on Friday began enforcing stricter rules on inspecting imported Japanese food products potentially originating in radiation-exposed areas, prompting a warning from Tokyo that it may call on the World Trade Organization for a ruling unless the restrictions are eased.

The new rules will only allow foods with Japanese government-issued place of origin certificates to enter Taiwan. On top of that, certain items from designated places in Japan will need radiation testing reports before they are granted access into Taiwan markets.

Taiwan’s Food and Drug Administration said the latest enforcement was in line with radiation safety management practices that other countries have put in place on Japanese food imports following the 2011 Fukushima nuclear disaster.

It said it is “necessary to protect the safety of food consumption” for Taiwanese.

But Japan is protesting the move, with the government warning that it may escalate the matter to the WTO, potentially deepening the conflict between Taipei and Tokyo.

“Japan’s government would like to urge Taiwan to scrap or ease the import restrictions based on scientific perspective,” said Yoshihide Suga, Japan’s top government spokesman said at a news conference on Friday in Tokyo.

His comments follow a similar message from Agricultural Minister Yoshimasa Hayashi on Tuesday that Tokyo may look to involve the WTO if Taiwan didn’t ease off on its regulations.

In January, Fukushima rice passed Japan’s radiation checks for the first time since the 2011 crisis.

Earlier this year, Taiwanese authorities said that more than 200 Japanese food products sold on the island originally came from radiation exposed areas near Fukushima Dai-ichi, but were mislabeled as having come from other areas.

Health officials at the time indicated they discovered suspect labeling by importers of Japanese food products, including Chinese-language labels carrying different places of origin that were stuck to mask the products’ domestic Japanese labels.

Taiwanese media reported in March that food products, from the Japanese prefectures of Fukushima, Ibaraki, Gumma and Chiba, which were banned in Taiwan since March 2011, had crept into local supermarkets due to the mislabeling.

Taiwan is the third-largest market for Japanese exports of food and agricultural, forest and fishery products.